Durable plain bearings and rolling bearings: How purposeful material selection minimizes friction, wear and corrosion

Bearings are central functional components in almost all machines and systems. However, their service life depends not only on design and lubrication, but significantly on an often underestimated factor: the right material pairing. Friction, wear, and corrosion are among the most common causes of bearing failure, with significant consequences for efficiency, maintenance, and operational safety. Understanding their causes and already counteracting these in a purposeful way in the material selection can extend service life, minimize energy losses, and increase the reliability of entire systems. In this article, we show how basic tribological principles, suitable metal pairings, and purposeful protective measures work together – and why the choice of materials in bearing technology is far more than merely a strength decision.

What are plain bearings and rolling bearings?

Bearings perform a central function in almost every machine: they allow the movement of rotating or linear components while simultaneously absorbing and transferring forces. There are two main types: Rolling bearings and plain bearings.

Rolling bearings consist of an inner and an outer ring, between which rolling elements – for example, balls or rollers – run. This design minimizes friction and allows precise motion at high speeds. They are common in powertrains, electric motors, and transmissions. Plain bearings, on the other hand, do not use rolling elements. Instead, a bearing surface slides directly on a mating surface, usually separated by a lubricating film. Plain bearings are particularly suited for applications with oscillating motion, high loads, or difficult environmental conditions.

For more information on different bearing types, see our article on the differences between plain bearings and ball bearings.

Importance of Material Pairings in Bearing Contact

For rolling bearings or plain bearings alike, the contact surfaces between the bearing and the mating body are crucial for the tribological behavior of the system. It is precisely at these points where two materials meet that they are permanently subjected to mechanical loads, generate friction, and are exposed to thermal stress. The correct material pairing is therefore not a secondary aspect, but an important criterion for functional reliability, energy efficiency, and service life.

Metallic material pairings are used wherever machine elements move relative to each other while being subjected to mechanical loads. In bearing applications, this means specifically: shafts rotate, slide, or oscillate in a bearing, where two metallic surfaces touch – often under high load, temperature, speed, or harsh environmental conditions. These contact zones are hotspots for friction, wear, and potential corrosion mechanisms. It becomes particularly critical if the lubricating film is interrupted, if micromovements occur (e.g. due to vibrations), or if aggressive media are present. In such cases, the material combination directly determines whether the bearing functions reliably or fails prematurely. Choosing the right metallic pairing influences:

• Friction loss
• Wear behavior
• Susceptibility to corrosion
• Emergency running properties

Understanding Tribology – a Definition

Where machine parts move and touch, forces arise that also generate friction, wear, and often unwanted energy losses. This is where tribology has its origins: it is the interdisciplinary science of friction, lubrication, and wear. In bearing applications, it is key to understanding why certain materials work better together than others.

Friction

Friction is the force that counteracts the relative movement of two bodies when in contact. It is created at the contact surfaces by mechanical interactions such as deformation and adhesion.

The coefficient of friction depends heavily on the material properties of the contact partners, in particular their surface hardness, roughness, chemical affinity and the ability to allow a stable lubricating film to form. Materials with a high tendency for adhesion (e.g. aluminum on steel) produce significantly higher friction than tribologically matched pairings (e.g. steel on bronze).

Wear

Wear refers to the progressive loss of material on a surface due to mechanical, thermal or chemical stress induced by relative movement. It is an irreversible process that results in wear, shape change, or loss of function.

Wear behavior is significantly determined by the combination of materials: Their hardness, ductility, microstructure and oxidation behavior affect how resistant they are to adhesion, abrasion or friction corrosion. Unsuitable material pairings can cause excessive wear even with good lubrication.

Lubrication

Lubrication is the purposeful introduction of a medium - usually a lubricant - between two contact surfaces to minimize friction and wear. A stable lubricating film should be built up, which largely prevents direct contact with the materials.

The effectiveness of lubrication depends on the surface energy, structure and wettability of the materials. Some materials (e.g., bronze or PTFE composites) promote uniform lubricating film formation, while others (e.g., very smooth, reactive metal surfaces) are more likely to have the lubricating film shear-off or chemically react with the lubricant.

Static friction and sliding friction - types of friction and their importance for bearings

Friction is a significant phenomenon in any bearing. It occurs when two bodies are in contact and move or attempt to move relative to each other. Different types of friction are distinguished, each of which acts differently and also places different requirements on materials and lubrication.

Static friction

Static friction is the frictional force that acts between two solid bodies before they move relative to each other. In bearing technology, it plays an important role, especially in the start-up of plain bearings or in oscillating movements. It is usually higher than sliding friction and can lead to a jerky start of movement – the so-called stick-slip effect.

The magnitude of this friction is described by the coefficient of static friction, which varies greatly depending on the material pairing. Material combinations with a high tendency to adhesion, such as aluminum on steel, have a particularly high coefficient of static friction. This increases the risk of unwanted micro-movements and uneven motion transitions. Purposeful material selection with matched surface properties and suitable lubricants helps minimize this effect and ensure stable operating conditions.

Sliding friction

Sliding friction occurs as soon as two solid bodies continuously move against each other after overcoming static friction – this transition from static friction to sliding friction is particularly relevant during start-up processes in plain bearings. In this case, sliding friction represents the dominant form of friction.

The coefficient of friction is influenced by many parameters, especially the surface roughness, the chemical reactivity of the contact partners, and their lubrication behavior. Material pairings with good sliding and run-in properties – for example, steel on bronze – allow a smooth friction transition, have low friction values, and lead to minimal wear. By carefully matching the materials, not only can the friction loss be reduced during the transition from static friction to sliding friction, but the heat generation and material wear during ongoing operation can also be significantly limited.

Rolling friction

Rolling friction occurs when one body rolls over another, such as balls or cylinders in rolling bearings.

It is significantly lower compared to sliding friction since the contact between the bodies is only point or line shaped. Nevertheless, rolling friction is not negligible – especially at high speeds or with insufficient lubrication. Material selection influences rolling friction based on hardness, dimensional stability, and lubricating film formation on the raceways. Hardened roller bearing steels with precision-machined surfaces help minimize rolling friction and extend bearing life.

Fretting corrosion

Fretting corrosion is a special form of friction that results from microscopic relative movements under load – usually in seemingly “stationary” connections. Typical locations are bearing fits, bolted joints, or shaft seats that are subject to varying loads or vibrations. These movements combine mechanical abrasion and chemical reaction with oxygen to create oxide particles that act like abrasives and accelerate wear. Fretting corrosion occurs more frequently when the material pairing is not matched, for example with large differences in thermal expansion behavior or with reactive metals without surface protection.

Material Pairings and Their Effect on Wear

The selection of suited material pairings is crucial when it comes to minimizing wear in bearing locations. This is because microscopic loads are created where two metals come into contact with each other during movement, which can lead to wear (abrasion) or local material transfer (adhesion) in the long term, especially due to poor lubrication or changing operating conditions.

Hardness relationship

A key criterion is the hardness relatiosnhip of the two contact partners. If the difference is too small, there is a risk of cold welding, especially in metallurgically similar materials. If the difference is too large, the harder material can abrasively grind down the softer partner, like an abrasive. An optimal combination usually consists of a hard, dimensionally stable material (e.g. hardened steel) and a softer, sliding partner (e.g. bronze or sintered metal), which can absorb particles without damaging the mating surface.

For a detailed overview of common hardening processes, please refer to our tech blog on steel hardening processes.

Chemical Affinity and Adhesion

An often underestimated parameter is the chemical affinity of two metals. Materials with similar electronic structure or lattice structure – such as aluminum and steel – tend to locally bond under frictional contact. This adhesion behavior can lead to material transfer, microwelding, and, as a result, increased wear. Therefore, material pairs should be specifically selected such that the tendency for adhesion is as low as possible. Lead, tin or graphite content in plain bearing materials often acts as “sliding modifiers”.

Oxide layers

Metals react with oxygen in the air to form oxide layers that may be beneficial or harmful depending on the material and environment. Stable, lubricating oxides, such as those found in lead bronze, are protective and aid in lubrication. By contrast, hard, abrasive oxides, such as aluminum oxide, can behave like abrasives and damage the mating surface. Therefore, it is important to consider not only the base material, but also its surface behavior in actual use when selecting materials.

Good versus bad material pairings

Proven material pairings are:

• Steel on Bronze: A classic, robust combination with good sliding properties, low adhesion, and high wear resistance – ideal for dynamically loaded plain bearings with intermittent lubrication.
• Steel on lead bronze or white metal: Very good sliding behavior, with a self-lubricating effect from soft components (e.g. lead, tin) – well suited for bearings with emergency running capability or shock-like loads.
• Steel on sintered metal: Porous bearing material that stores lubricant – especially efficient for low-maintenance bearing locations with limited lubrication access.
• Steel on PTFE: Excellent in dry running applications or in extreme friction conditions – the plastic component greatly reduces friction.

Critical or unfavorable pairings are:

• Steel on aluminum: High adhesion tendency, formation of hard aluminum oxides, prone to fretting corrosion – unsuitable without coating or purposeful lubrication measures.
• Steel on stainless steel: Two hard, noble metals with strong affinity for cold welding - high friction values, risk of galling, especially on insufficient lubrication.
• Stainless steel on copper or brass: Prone to chemical corrosion - increased risk of bimetallic corrosion, especially in moisture or electrochemically active environments.
• Aluminum on aluminum (same or similar alloy): Extremely high tendency to adhesion and galling, very unfavorable for sliding contacts - should generally be avoided, except when separated by suitable coating or polymer film.

Measures to protect against friction, wear and corrosion in plain bearings and rolling bearings

Forces, movements and environmental influences act together in any bearing point. Friction, wear and corrosion are not preventable, but they can be reduced in a purposeful manner. For more detailed information, see our article on erosion and corrosion in mechanical engineering. A holistic approach that equally takes into account material selection, surface treatment, lubrication and design is effective. The following measures demonstrate how to effectively control these tribological challenges in practice.

Control wear by specifically selecting a “sacrificial part”

In many technical applications, it is not economically reasonable to design all bearing components for maximum wear resistance. Instead, the design often follows the principle of planned weakening in the right place: by deliberately selecting a “sacrificial part” within the bearing pairing. The sacrificial part is the technically and economically more easily replaceable or regenerable component of the friction pairing - usually the bearing bushing, sliding plate or bearing shell, less often the shaft or the housing.

The goal is to focus the inevitable wear on this part to:

• avoid damage to more expensive, difficult-to-replace parts (e.g. shaft, housing bore),
• to make maintenance predictable and cost-efficient,
• and extend the overall service life of the system by simply replacement.

Selecting a “sacrificial part” is a proven method in bearing technology to balance function, service life and maintenance costs. Instead of maximum wear resistance at all points, purposeful, controlled material degradation is used where it is technically reasonable and economically justifiable. Examples include:

• Steel shaft and bronze bushing: The bronze bushing is softer and has better sliding properties - it wears deliberately but can be easily replaced without damaging the hardened shaft. Tips on the appropriate fit are provided by our article on the basics of dimensional tolerances and fit selection.
• Housing with replaceable bearing shell (e.g. white metal): In high-load applications, inserts are used to make the soft bearing material deliberately sacrificial.
• Sintered metal or plastic plain bearings in sheet metal housings: The bearing itself is an inexpensive wear element that can be replaced quickly during the maintenance interval.

Other protective measures

In addition to the purposeful selection of a “sacrificial part” as a replaceable wear component, many other protective measures are available in bearing technology to minimize friction, wear and corrosion. These include, among other things, matching material pairings, wear-resistant coatings, the optimization of surface roughness, the use of suitable lubricants as well as constructive measures such as sealing systems or insulating intermediate layers. From sintered metal bearings with built-in lubricant reservoir, to corrosion-resistant bearing shells, or precisely matched fits to prevent friction corrosion: these approaches combine to create long-lasting, maintenance-friendly, and cost-effective bearing solutions.